In the operation of a multi-unit rotary offset printing press, freshly printed substrates such as sheets or web material are guided by transfer cylinders or the like from one printing unit to another, and then they are delivered to a sheet stacker or to a sheet folder/cutter unit, respectively. Transfer cylinders are know by various names including delivery cylinders, transfer rollers, support rollers, delivery wheels, skeleton wheels, segmented wheels, transfer drums, support drums, spider wheels, support wheels, guide wheels, guide rollers, etc. The ink marking problem inherent in transferring freshly printed substrates have been longstanding. Numerous efforts to solve the ink marking have been made. Some of them are discussed in U.S. Pat. Nos. 4,402,267 and 6,244,178, which are hereby incorporated for all purposes.
U.S. Pat. No. 4,402,267, disclosed an anti-marking fabric covering system for transfer cylinders. The system included the use of a low friction coating on the supporting surface of a transfer cylinder, over which was loosely attached a movable fabric covering. A suitable fabric covering was a loosely woven, lightweight cotton material such as gauze. The fabric was prepared by washing in water in the presence of a suitable fabric softener dissolved in the water. After the fabric was dried, a suitable fabric protector was applied to enhance the liquid repellency characteristics of the material. The fabric could then be attached to the transfer cylinder by the use of fastener strips such as the hook portion of a hook and loop type fastener system such as that made under the trademark VELCRO.
U.S. Pat. No. 6,244,178 disclosed numerous improvements to the flexible jacket covering. It disclosed use of cotton cheesecloth which is bleached, dyed, treated with an ink repellent and treated with an antistatic ionic polymer compound or otherwise rendered conductive. The covering was also preferably prestretched, and cut to a size having length and width dimensions corresponding to dimensions of a transfer cylinder, or in some embodiments to the smallest sheet size that is expected to be printed. The flexible jacket covering was then attached to the transfer cylinder by pressing onto VELCRO fastener strips which were attached to the cylinder.
The flexible jacket coverings used in the two above referenced patents were originally made from fabric woven on conventional shuttle looms. With shuttle looms, the weft threads are continuous and are woven back and forth through the loom shed. At each edge of the fabric, the weft threads form a loop around the outermost warp threads, thereby forming a stable edge which will not unravel even when it is processed as described above.
The textile industry has been changing to shuttleless looms which are also referred to as fluid weft insertion looms, air jet looms, etc. As the names suggest, these looms do not use a mechanical shuttle. Instead, they use air jets to insert weft threads into and across the shed of warp threads. With this type of loom, the weft threads are inserted as separate segments of thread extending across the loom and having free ends at each edge of the fabric. To prevent unraveling at the edges, various systems have been developed for forming a selvage along the edges of the fabric. One way of forming a selvage is to provide an extra length of thread at the end of each weft thread and to fold it back into the shed along with the insertion of the next weft thread. The tucking method may be combined with other techniques, such as leno stitches, to provide a stronger selvage.
As discussed in U.S. Pat. Nos. 4,402,267 and 6,244,178, a fabric preferred for use as flexible jacket coverings is a loosely woven cotton fabric like gauze or cheesecloth having a thread density of about 32 threads per inch in the warp direction and about 28 threads per inch in the weft direction. In order to form a strong selvage in loose weave fabric, it is standard practice in the textile industry to substantially increase the density of warp threads in the selvage area of the fabric. For example, two threads may be included in each dent in the selvage area, thus increasing the warp thread density to about 64 threads per inch. With a warp thread density such as this, the tucked weft threads are firmly held in the selvage and do not unravel as the fabric is processed to become a flexible jacket covering.
While the conventional selvage works as intended to prevent unraveling, it has created problems in the making and use of flexible jacket coverings. As indicated above, the woven fabric is processed through a number of steps in the making of flexible jacket coverings. It is desirable to use all of the processed fabric to avoid waste. One way of avoiding waste is to include the selvage as part of the flexible jacket covering. With the fabric woven on shuttle looms, the original fabric edge was used as a jacket covering edge which was attached to the VELCRO fastener strips. However, with fabric woven on shuttleless looms, the conventional high-density selvage has proven to be less suitable for attachment to the VELCRO fastener strips. The high-density selvage typically will not grip if attached with normal hand pressure. If enough force is used to form a tight grip on the VELCRO strips, then it is difficult to remove the jacket coverings when they need to be replaced. As a result, it has been found necessary to cut the selvage from the fabric and use a portion of the body of the cloth to attach to the VELCRO fastener strips. The fabric must have a hem stitch sewed along the cut edge to avoid unraveling of the cut edge during processing and handling. Thus the conventional shuttleless loom high density selvage causes less efficient use of the fabric and requires an additional process step.